Prenden, Germany — At a forlorn bus stop 45 minutes outside Berlin, a faded schedule lists service to the suburbs. Voices drifting out of a workshop are the only signs of life in this 500-person town.

Nothing indicates that in the forest just a few hundred yards away is an underground bunker built to save elite East German leaders from a nuclear attack. The concrete-and-steel structure serves as a powerful reminder of the prospect of mutually assured nuclear annihilation when the US and USSR faced off in Berlin during the cold war.

The bunker will briefly drop its veil of secrecy this August, as a volunteer group opens it for three months to give the general public their first and final chance to see this bastion of a bygone era. It will then be permanently sealed.

"The neighbors knew something was here then, but not what. They thought it was a missile base," explains Hannes Hensel, a photographer and leader of the Berlin Bunker Network (BBN), the volunteer group organizing tours of the bunker.

For more than two years, Mr. Hensel has traveled several times a week to the locked gate and dirt path that mark the way to the bunker.

The entrance is little more than a trapdoor in the tunnel ceiling. Hensel, a tall and sturdy climber who rappelled the walls to snap hundreds of panoramic photographs, swings easily to the muddy concrete floor and sets up a ladder.

He and other BBN members shot some 1,500 photos of the three-story, 7,500-square-meter bunker, which they plan to publish online by 2010.

Authorities in Berlin have struggled to prevent break-ins since the bunker was initially sealed in 1993. BBN assumed responsibility for securing the bunker and sealing it permanently in exchange for the right to conduct tours and photograph the interior.

The Prenden facility was designed to shelter about 400 people for two weeks, including Erich Honecker, who led the former German Democratic Republic (GDR) from 1971 to 1989, and was responsible for building the Berlin Wall.

The bunker comprises a series of containers suspended by huge cables inside a concrete shell. An 11-foot-thick blast cap would have protected from all attacks but a direct bomb strike.

The facility is one of many built by an East German leadership in the late 1970s and 1980s, fearful that the policy of detente between cold war powers was merely a front for a Western attack plan, says Rainer Eckert, director of the Forum for Contemporary History.

"It's a little strange. The GDR was about to collapse, the revolution was coming, and even as the economy was doing badly, they were building these bunkers," Mr. Eckert says. "It's a paradox in history."